1. Technical Field
The present invention is directed generally to a railway short span trestle and more particularly to such a trestle which may be preassembled in the shop for delivery of a minimum number of parts to a site for quick efficient erection and installation onto the substructure.
2. Description of the Prior Art
The replacement of old existing short span railway trestles is a necessary part of track maintenance both because of the age of existing trestles and the insufficient load limits for which they were designed. Existing steel trestles were most commonly assembled by field welding all parts. That was extremely time consuming, labor intensive and expensive. The custom design of each trestle for a given site further complicated erection, installation and subsequent repairs became of the many non-standard parts. Another disadvantage of existing short span trestles is that they generally required pile bents every 20 or 30 feet.
An important consideration in trestle replacement is to minimize track down time. Replacement of steel trestles with prefabricated concrete trestles may result in a substantial increase in the vertical distance between the ballast deck plate and the bottom of the trestle thereby requiring road work leading up to the trestle from both sides and the substantial expense and down time associated therewith. Road work over approximately 800 feet of track may be required to accommodate a 11/2 foot rise in the track due to trestle replacement with trestles of precast concrete construction. The precast concrete replacement trestles are very heavy and require bigger and perhaps multiple cranes in the field for installation.
Further problems associated with replacement of existing railway short span trestles with conventional trestles are that the existing trestle often needs to be removed or modified before construction of piles for the new trestle, thereby substantially increasing track down time and/or requiring a reduction of allowable train speeds across an existing trestle. Finally, it is a perpetually difficult task to transport, organize, and find all of the custom parts that need to be field welded together at the site for construction of a replacement steel trestle.
Accordingly, a primary object of the present invention is to provide an improved railway short span trestle and method of installation.
Another object is to provide such an improved trestle and method which enable minimum track down time for trestle replacement.
A more specific object is to provide such a trestle and method which enable piles for a new trestle to be driven outside of the existing structure prior to removal of the existing structure.
A related specific object of the invention is to provide such a trestle and method which enable the new trestle to be assembled off-pier for placement as a single unit onto new pile caps.
Another object is to provide such a trestle and method which result in a steel trestle weighing substantially less than a comparable concrete span.
A related object is to provide such a trestle and method which require fewer or a smaller crane in the field for the trestle replacement operation.
Another object is to provide such a trestle and method with a minimum number of parts to be assembled in the field.
A related specific object is to provide such a trestle and method which enable stocking standard floor assemblies which may be assembled in various combinations for given span lengths.
Another related specific object is to provide such a trestle and method which minimize required field labor for trestle replacement.
A related specific object of the invention is to provide an improved trestle and method with high quality welds due to substantial shop welding of subassemblies prior to delivery of those subassemblies to a site.
Another object of the invention is to provide such a trestle and method which enable quick delivery of replacement parts due to prefabrication of standard subassemblies and storage of those parts at multiple sites.
Another object of the invention is to provide such a trestle and method which provides a trestle with minimum vertical distance from the top of the ballast floor plate to the bottom of the girders.
A related specific object of the invention is to provide such a trestle and method wherein the distance from the top of the ballast floor plate to the bottom of the girder is less than 2 feet.
A related specific object of the invention is to provide such a trestle and method which require minimum road work in any given trestle replacement.
Another object of the invention is to provide such a trestle and method with decreased substructure requirements, namely fewer bents of piles for lower cost.
A further object of the invention is to provide such a trestle and method which require little maintenance over the life of the trestle.
A final object of the invention is to provide an improved railway short span trestle which is simple and rugged in construction and efficient in operation.